1. Field of the Invention
The present invention relates to a carrying apparatus for carrying a semiconductor wafer or other thin sheet materials (hereinafter referred to as wafers) and, more specifically, it relates to an apparatus for carrying a wafer into and out of a heat treatment unit.
2. Description of the Prior Art
Examples of a wafer carrying apparatus of interest related to the present invention are disclosed in, for example, Japanese Patent Laying-Open Gazette No. 44721/1983 and in U.S. Pat. No. 4,591,044. The above mentioned U.S. Pat. No. 4,591,044, entitled "Apparatus for feeding wafers and the like" was issued to the assignee of the present invention on May 27, 1986. The referenced U.S. patent is incorporated herein by reference.
FIGS. 1A and 1B show an example of a conventional wafer transferring and carrying apparatus as in the referenced U.S. patent. FIG. 1A is a plan view of the apparatus and FIG. 1B is a cross sectional view taken along the line B--B in FIG. 1A.
The apparatus for feeding wafers comprises a carrying belt 3 for carrying a wafer 1, the belt 3 fitting in a trench 5 formed on the surface of a heat treatment plate 2, a pulley 9 for supporting the carrying belt 3, a push up pin 7 for easy detaching of wafer 1 from the heat treatment plate 2 after the heat treatment thereof and an air cylinder 8 for moving the push up pin 7 up and down. The heat treatment plate 2 has two types of through-holes, namely, a hole 4 having its end connected to a gas compressor and a hole 6 for moving the push up pin 7 up and down, in order to detach the wafer 1 easily from the heat treatment plate 2 after the heat treatment.
The wafer 1 is carried onto the heat treatment plate 2 by the carrying belt 3. At the time of carrying-in, the pulley 9 is raised so that the lower surface of the carrying belt 3 is apart from the surface of the heat treatment plate 2 and the carrying belt 3 moves freely.
When the wafer is carried onto a prescribed position on the heat treatment plate 2, the pulley 9 is lowered to the heat treatment plate. Consequently, the carrying belt 3 is lowered into the trench 5 that is formed in the heat treatment plate 2 as shown in FIG. 1B. The wafer 1 is then held on the heat treatment plate 2. When the heat treatment is completed, gas is ejected through the holes 4 and simultaneously the air cylinder 8 is driven to raise the push up pin 7 upward. The wafer 1 is then raised above the heat treatment plate 2. Thereafter, the carrying belt 3 is raised to a position enabling carrying of the wafer 1 and the belt receives the wafer 1 from the push up pin 7 to carry the same to a succeeding process.
However, since the above mentioned conventional apparatus for feeding wafers is provided with a belt guiding trench for receiving the wafer carrying belt on the upper surface of the heat treatment plate, it has various disadvantages. One of the disadvantages is that the temperature distribution of the wafer is not uniform. Another disadvantage is that dust collects on the trench and the dust may possibly adhere to the wafer via the wafer carrying belt. A further disadvantage is that the heat degrades the carrying belt shortening its life, since the temperature of the carrying belt varies greatly as it travels in and out of the trench.